Aircraft need to produce varying levels of lift for take-off, landing and cruise. A combination of wing leading and trailing edge devices are used to control the wing coefficient of lift. The leading edge device is known as a slat. On larger aircraft there may be several slats spaced along the wing edge. During normal flight the slats are retracted against the leading edge of the wing. However, during take-off and landing they are deployed forwardly of the wing so as to vary the airflow across and under the wing surfaces. The slats usually follow an arcuate or curved path between their stowed and deployed positions. By varying the extent to which the slat is deployed along said path, the lift provided by the wing can be controlled.
An assembly is required to support and guide movement of a slat between stowed and deployed positions and a typical arrangement showing a cross-section through part of a wing 1 and a slat 2 in its stowed position is illustrated in FIG. 1. As can be seen from FIG. 1, the slat 2 is provided with an arcuate support arm or slat track 3 one end 4 of which is attached to the rear of the slat 2 and extends into the wing 1. To allow for wing bending and manufacturing tolerances, the end 4 of the slat track 3 is attached to the slat using spherical bearings and linkages (not shown). The slat track 3 penetrates wing spar 6 forming the wing structure. The slat track 3 defines an arc having an axis and is mounted within the wing so that it can rotate about that axis (in the direction indicated by arrows “A” and “B” in FIG. 1) to deploy and retract the slat 2 attached to one end of the slat track 3.
To drive the slat track 3 so as to deploy or retract the slat 2, a toothed slat track rack 7 having an arcuate shape corresponding to the arcuate shape of the slat track 3 is mounted within a recess 3a on the slat track 3 and a correspondingly toothed drive pinion 8 is in engagement with the teeth 7a on the slat rack 7 so that when the drive pinion 8 rotates, the teeth 8a on the drive pinion 8 and the teeth 7a on the rack 7 cooperate to pivot or drive the slat rack 7 and the slat attached thereto, into a deployed position, i.e. in the direction of arrow “A” in FIG. 1. Typically, the slat track 3 rotates through an angle of 27 degrees between its fully stowed and fully deployed positions. Rotation of the pinion 8 in the opposite direction also drives the slat track 3, in the direction of arrow “B”, back into its stowed position, as shown in FIG. 1.
The drive pinion 8 is mounted on a shaft 9 that extends along, and within, the leading edge of the wing 1. Several gears 8 may be rotatably mounted on the shaft 8, one for driving each slat 2 so that when the shaft 9 is rotated by a slat deployment motor close to the inboard end of the wing t, all the slats are deployed together.
The slat track 3 is supported between roller bearings 10a, 10b both above and below the slat track 3 and the axis of rotation of each bearing 10a, 10b is parallel to the axis of rotation of each of the other bearings 10a, 10b and to the axis about which the slat track 3 rotates in the direction of arrows “A” and “B” between its stowed and deployed positions. The upper bearings 10a lie in contact with the upper surface 3b of the slat track 3 and the lower bearings 10b lie in contact with the lower surface 3c so that they support the slat track 3 and guide it during deployment and retraction. The bearings 10a, 10b resist vertical loads applied to the slat 2 during flight and also guide movement of the slat track 2 during slat deployment and retraction.
It will be appreciated that space for components within the wing structure close to the leading edge of the wing 1 is very limited. The requirement to house all these components places considerable design restrictions on the shape of the wing 1 in addition to increasing weight, manufacturing costs and complexities.
A further disadvantage with the conventional assembly described above is that the slat track 3 must be relatively long to accommodate the desired maximum deployment angle for the slat 2 whilst ensuring that the slat track 3 is adequately supported by two vertical load bearings 10a above the slat track 3 and two vertical load bearings 10b below the slat track 3, even at maximum deployment. As a result of its extended length, the slat track 3 penetrates the spar 6 and so the free end of the slat track 3 must be received within a track can 13 that separates the slat track 3 from the fuel stored within the wing 1 behind the spar 6. However, it is undesirable to have openings in the spar 6 as this can weaken the wing structure and so reduce its resistance to bending. It will also be appreciated that the requirement for a track can 13 also presents additional problems and assembly issues with the need to provide an adequate seal where the track can 13 is attached to the spar 6 so as to prevent fuel leakage.
The present invention seeks to provide a slat support and deployment assembly for an aircraft which does not penetrate the spar and so substantially overcomes or alleviates the problems referred to above.
An assembly which seeks to address the problems identified above has already been proposed and will now be described, prior to describing the slat support and deployment assembly of the present invention.
Referring to FIGS. 2 and 3, there is shown part of a structural rib 15 of an aircraft wing and a slat deployment assembly 16. The wing has a number of ribs 15 parallel to and spaced from each other along the length of the wing, although only two such ribs 15 are shown in FIGS. 2 and 3. Each rib 15 has an opening 17 therethrough in which is received and mounted a linear and rotary tube bearing (not shown).
The assembly 16 comprises a rigid tube 18 that extends along the length of the wing through the opening 17 in each rib 15. The tube 18 is received within the bearing in each rib 15 so that it is able to slide in a longitudinal direction (i.e. in the direction of axis ‘A’ in FIG. 2) through each rib 15 and also so that it can rotate about its longitudinal axis “A”. A drive motor (not shown) is mounted within the wing structure and is operable to slide and rotate the tube 18 during deployment and retraction of a slat.
Although the slat support assembly 16 may comprise only a single tube 18 driven by a single motor for simultaneous deployment of all the slats associated with a particular wing, it is envisaged that there may also be multiple tubes 18, each with their own drive motor, so that each or certain slats may be driven independently as required.
The slat support assembly 16 also comprises a linkage or scissor mechanism including a primary support arm 19 having a first end 19a connected to the tube 18 and a second end 19b for connection to a slat to be deployed. The slat support assembly 16 also includes a control arm 20 coupled between the rib 15 and the primary support arm 19 between its first and second ends 19a,19b, as will now be explained in more detail.
The tube 18 extends through a stirrup 21 formed at the first end 19a of the primary support arm 19 and the primary support arm 19 is pivotally coupled to the tube 18 so that the primary support arm 19 can rotate about an axis ‘B’ that extends through stub axles 22 that extend from diametrically opposite surfaces of the tube 18 and which are received in corresponding holes 23 formed in each leg portion 21a, 21b of the stirrup 21.
The second end of the primary support arm 19b has a cylindrical aperture 24 to receive a pivot pin (not shown) which is coupled to the inboard end of a slat (not shown) so that the primary support arm 19 and slat can rotate relative to each other about the longitudinal axis ‘C’ of this pin during deployment and retraction of the slat.
The control arm 20 comprises a hub 25 (see FIG. 3) which is received within an aperture 26 in the primary support arm 19 roughly midway between its first and second ends 19a, 19b. The hub 25 has a pin 27 that locates in holes 28 in the primary support arm 19 so that the primary and secondary support arms 19, 20 can rotate relative to each other about an axis D extending through the hub 25.
The control arm 20 has a forked arm sections 20a extending away from a body portion 20b pivotally connected to the hub 25 for rotation about an axis E (see FIG. 3). The forked arm sections 20a extend away from the body portion 20b at a divergent angle from each other. A minor hub 29 is formed at the end of each of the forked arm sections 20a and these minor hubs 29 are received within corresponding apertures 30 in the rib 15. The hubs 29 are pivotally coupled to the rib 15 using pins (not shown) that extend through the rib 15 into the each hub 29 so that the control arm 20 can pivot relative to the rib 15 about an axis ‘F’ that intersects the longitudinal axis A of the tube 18.
It will be noted that the axes ‘C’ and ‘D’ are parallel to each other and remain so during deployment and retraction of a slat. However, axis ‘F’ extends at an angle relative to axes ‘C’ and ‘D’ i.e. it is displaced through a compound angle in both directions so that it is rotated about the longitudinal axis ‘A’ of the tube as well as being displaced through an angle such that it not perpendicular to the longitudinal axis ‘A’ of the tube. This arrangement produces an arcuate path to the free end of the primary support arm 19 when the tube 18 is both slid laterally and rotated about its longitudinal axis ‘A’.
To deploy a slat from an aircraft wing that has been coupled using the above-described mechanism, the motor is driven so as to cause the tube 18 to slide in a longitudinal direction through the bearings (i.e. in the direction of arrow “P”). In addition to the sliding movement of the tube 18, the motor is also configured so as to cause simultaneous rotation of the tube 18 about its longitudinal axis ‘A’, through an angle that is in the region of 15 degrees. This longitudinal and rotational movement of the tube 18 causes the primary support arm 19 to rotate relative to the tube 18 about the axis ‘B’ and relative to the control arm 20 about the axis D. Furthermore, the body portion 20b of the control arm 20 rotates relative to the hub 25 about axis ‘E’ and the hubs 29 rotate relative to the rib 15 about axis ‘F’ so that the end 19b of the primary support arm 19 moves in a direction away from the tube 18 (as indicated by arrow “X” in FIG. 2) in an arcuate path so as to deploy the slat laterally from the wing edge, the primary support arm 19 also rotating relative to the slat about axis ‘C’ during this movement.
The primary support arm 19 moves in the opposite direction when the motor is driven in reverse so as to slide the tube 18 in the opposite direction so as to retract the slat.
It will be appreciated that the primary support member 19 and the control arm 20 both rotate together with the tube 18, such that the axes B, C and D all remain parallel throughout the rotational movement of the tube 18.
Although the above-described slat control mechanism overcomes or alleviates some of the disadvantages of the conventional support assembly, as it does not penetrate a spar or require a track can extending into the fuel tank within the wing structure, it still presents a number of drawbacks. In particular, the bearings received within the ribs must be capable of withstanding sliding and rotational motion as well as spherical movement to accommodate misalignment driven by wing bending and manufacturing tolerances, thereby increasing complexity and wear characteristics.
The present invention seeks to provide a slat support assembly that overcomes or substantially alleviates the disadvantages with the assembly described in more detail above.